So-called "associative thickeners" have been exploited commercially in a wide range of coatings recently. Such thickeners show many advantages in emulsion paints over traditional thickeners, such as cellulosics and non-associative alkali-soluble acrylics, including better flow and levelling, improved application characteristics especially with rollers and good water resistance. A common feature of these associative thickeners is that they comprise molecules that contain both hydrophilic and hydrophobic sections. The hydrophilic parts maintain the solubility of the molecule in the aqueous phase whilst the hydrophobic parts have a tendency to associate with the hydrophobic parts of dissolved or dispersed materials.
One of the most economical types of prior art associative thickener is based on a copolymer of various (meth) acrylates and (meth) acrylic acid which has been modified to give branches from the main polymer chain consisting of a hydrophilic polyethylene oxide chain tipped by a moderately large hydrophobic group. Such associative branches are commonly introduced by the use of a monomer comprising an ester of a polymerisable mono- or di-carboxylic acid and a hydroxy terminated non-ionic surfactant. This class of monomer can be described by the formula: EQU R.sub.1 [CO.sub.2 -(CH.sub.2 CH.sub.2 O).sub.n -R.sub.2 ].sub.m
Where R.sub.1 is an ethenyl or ethenylene group such as
CH.sub.2 .dbd.CH-- PA1 CH.sub.2 .dbd.C(CH.sub.3)-- PA1 --CH.dbd.CH-- PA1 --CH.dbd.C(CH.sub.3)-- PA1 n is an integer between 10 and 100 PA1 m=1 for when R.sub.1 is ethenyl and m=2 when R.sub.1 is ethenylene PA1 R.sub.2 is the hydrophobic part of the molecule which is commonly a C.sub.12 to C.sub.25 alkyl group, an alkyl (C.sub.8 -C.sub.9) phenyl or a polyalkylene (C.sub.3 or C.sub.4) oxide chain. PA1 R.sub.1 is CH.sub.2 .dbd.CH-- or CH.sub.2 =C(CH.sub.3)-- PA1 n=6-100; m=1 PA1 R.sub.2 is alkyl phenol or propoxylated alkyl phenol PA1 R.sub.1 is CH.sub.2 .dbd.CH-- or CH.sub.2 .dbd.C(CH.sub.3)-- PA1 n=8-60; m=1 PA1 R.sub.2 is C.sub.12 -C.sub.18 alkyl PA1 R.sub.1 is --CH.dbd.CH-- or --CH.dbd.C(CH.sub.3)-- PA1 n=10-70; m=2 PA1 R.sub.2 is alkyl phenol PA1 R.sub.1 is ##STR2## n=(unspecified); m=1 R.sub.2 is C.sub.18 alkyl PA1 A=H, --(CH.sub.2 CH.sub.2 --O).sub.n --R, C.sub.1 -C.sub.20 alkyl, --(CH.sub.2 CH.sub.2 --O).sub.m --H or --(CH.sub.2 CH.sub.2 --O).sub.m --CH.sub.3 PA1 (d) 0-1.0% of a polyethylenically unsaturated monomer which is effective for chain branching or crosslinking PA1 (e) Not more than 10% of an ethylenically unsaturated hydrophylic monomer as an optional, but preferred, component, PA1 n is an integer between 5 and 20.
The patent literature shows that several combinations of these components have already been recognised as having the potential for use in thickeners:
EP No. 0 011 806 (Dow) suggests: PA0 EP No. 0 013 836 (Rohm and Haas) recommends: PA0 GB No. 2 127 836 (Uniroyal) defines useful materials where: PA0 JA No. 83 180 510 (Toyo Soda); Chem Abs. 1984 100 104062 suggests: PA0 (a) 25-45% methacrylic acid, acrylic acid or a mixture thereof; PA0 (b) 25-65% alkyl acrylate, alkyl methacrylate or mixture thereof; PA0 (c) 1-40% of an ester of composition ##STR3## in which R is a C.sub.12 -C.sub.25 alkyl n=at least 10; m=at least 5